1. Field of the Invention
The present invention generally relates to mechanical press fit pipe joints, and more particularly to a computer-implemented system and method for measuring and monitoring parameters of press fit mechanical pipe joints during both manufacturing and assembly of pipe segments, the construction of pipelines, monitoring environmental conditions and stresses experienced by the mechanical press-fit pipe joints, and utilizing the data produced thereby to formulate standards for mechanically joined pipe segments.
2. Background of the Invention and Description of the Prior Art
Pipelines for conveying commodities and other substances—typically fluid materials, including oil and liquid products refined therefrom, as well as natural gas, compressed gas, and CO2 to name some examples—over long distances are subject to a variety of conditions and forces that can act to cause failures in the pipeline such as breaks, ruptures, or leaks. These failures may be expressed by tension or compression forces exerted on the joint, or by bending, twisting, or vibration of the pipeline, etc., generally due to excessive internal pressures or geological or meteorological conditions present at the location of the pipeline. A pipeline is typically constructed of sections of pipe joined together end-to-end by various means. The utility, integrity, and longevity of the pipeline in the widely varying conditions noted above depends critically on the quality of the joints. A variety of methods are used to join the pipe sections together, including but not limited to welding, threaded joints, cemented joints, and mechanical joints.
While capable of providing secure, reliable, and durable joints, the more common methods of welding, threading, and cementing involve relatively time-consuming, labor-intensive operations during manufacture or preparation such as the welding operation itself, machining the pipe ends to cut the threads, honing and cleaning the surfaces to be joined when cements or epoxy materials are used to join the sections together. These operations may extend the time to install a pipeline, and increase the costs of construction, thereby reducing the productivity of the enterprise. Mechanical press fit joints, on the other hand, offer the potential for rapid construction at much lower costs, eliminating a substantial portion of the labor-intensive work of the traditional methods of joining pipe sections together. In a mechanical joint the end of one section of pipe, slightly enlarged (called a “bell” or “box” end) is forced—i.e., press fit—over the adjoining end of the other section, which may be slightly tapered (called a “pin” end) to accommodate the passage of the box end over the pin end. Typically the ends thus pre-shaped are aligned and hydraulically pressed together until a prescribed amount of overlap of the box end of a first pipe segment over the pin end of the adjoining pipe segment is achieved. Mechanical joints thus formed are rapidly made, resulting in much less time to construct a pipeline, usually involving fewer workers.
However, mechanical joints rely principally on the uniformity and area of contact along the interface between the pipe ends pressed together, one over the other, to provide and maintain the leak-proof integrity of the joints. To an observer during assembly of mechanical pipe joints, the only parameter of interest appears to be the amount of overlap of the two pipe ends under the pressure employed to assemble the joint, which is not subject to measurement during assembly. However, this parameter does not take into account variations in the tooling (e.g., due to wear or failure to maintain dimensions within tolerance), deformation of the pin or box ends of the pipe sections as may be caused by dropping the pipe sections on end during loading or unloading, defects in the surface of the contact areas of the pipe sections to be joined (e.g., scratches or corrosion), the ambient temperature at the site of joint making, or the temperature of the pipe sections at the time of joint making, for example. Moreover, typical assembly practices include no significant preparation of the pipe ends such as cleaning, inspecting, etc. to ensure that the pipe joint will have adequate strength and integrity over its useful life.
As a result, mechanical joints are found less often in pipelines designed for conveying flammable or toxic materials, for example, where failures may be catastrophic, damaging the environment, causing injury, disease, or death, etc. Moreover, the conventional method of gauging the correct assembly of box-to-pin ends of pipe sections—marking the pin end of one section to be joined with paint, wax, or chalk a few inches from the end to indicate how far the box end of the other section to be joined should overlap the pin end—leaves much to be desired in terms of repeatability and consistency because of the reliance on a single, hand-applied mark and the manual coordination of the operators that inscribe the mark, and apply the pressure to join the sections. While this method is quick, the margin of potential error is substantial, and likely insufficient to guarantee the integrity of the joint under all field conditions, particularly if the pipe sections are out of spec as to their dimensions, have defects or anomalies due to corrosion, deformation (e.g., departure from roundness), scoring, etc. More importantly, there is no measure of the integrity of the joint, no traceable record or data of the joint or its assembly, no direct and verifiable relationship between the proximity of the end of the box section to the mark on the pin section and the ability of the joint thus formed to withstand the conditions of use in the pipeline.
Some potential for errors can be reduced through testing of sample joints in a laboratory, using tests for pressure, tension, compression, bending, and perhaps twisting, temperature cycling, or vibration for example. Assembly workers can measure the distance of the internal shoulder in the box or bell end from the end of the pipe (if one has been machined therein) and use that dimension to place the mark in the pin end. However, even though such tests may be performed under controlled conditions, it is impractical to simulate all of the variables that can occur in an actual installed pipeline, over the life of the pipeline. Because press fit mechanically joined pipe tends to lack the same degree of metal-to-metal contact that is considered inherent in welded or threaded joints, ways to demonstrate the integrity and strength of press fit joints are needed so that mechanically joined pipe can compete effectively with the traditional methods.
In the face of such simplicity and potential for error, and the lack of performance measures for mechanical pipe joints, what is needed are improved methods for mechanically joining pipe sections together and improvements in the methods for measuring the relevant parameters of a mechanical joint to ensure that a joint of high quality, integrity, and consistency is formed at each joint in a pipeline, and that enable the retrievable collection of data about the joints thus formed both as to the original assembly of the joints and the performance of the joints in situ over time. Improvements must demonstrate superior performance at substantially reduced costs to become viable alternatives to the traditional methods of welding, screw threads, or cementing the pipe sections together.